Murakami M, Kambe T, Shimbara S, Higashino K, Hanasaki K, Arita H, Horiguchi M, Arita M, Arai H, Inoue K, Kudo I
Department of Health Chemistry, School of Pharmaceutical Sciences, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142, Japan.
J Biol Chem. 1999 Oct 29;274(44):31435-44. doi: 10.1074/jbc.274.44.31435.
We have recently reported that members of the heparin-binding group II subfamily of secretory PLA(2)s (sPLA(2)s) (types IIA and V), when transfected into 293 cells, released [(3)H]arachidonic acid (AA) preferentially in response to interleukin-1 (IL-1) and acted as "signaling" PLA(2)s that were functionally coupled with prostaglandin biosynthesis. Here we show that these group II subfamily sPLA(2)s and the type X sPLA(2) behave in a different manner, the former being more efficiently coupled with the prostaglandin-biosynthetic pathway than the latter, in 293 transfectants. Type X sPLA(2), which bound only minimally to cell surface proteoglycans, augmented the release of both [(3)H]AA and [(3)H]oleic acid in the presence of serum but not IL-1. Both types IIA and V sPLA(2), the AA released by which was efficiently converted to prostaglandin E(2), markedly augmented IL-1-induced expression of cyclooxygenase (COX)-2 in a heparin-sensitive fashion, whereas type X sPLA(2) lacked the ability to augment COX-2 expression, thereby exhibiting the poor prostaglandin E(2)-biosynthetic response unless either of the COX isozymes was forcibly introduced into type X sPLA(2)-expressing cells. Implication of phospholipid scramblase, an enzyme responsible for the perturbation of plasma membrane asymmetry, revealed that the scramblase-transfected cells became more sensitive to types IIA and V, but not X, sPLA(2), releasing both [(3)H]AA and [(3)H]oleic acid in an IL-1-independent manner. Thus, although phospholipid scramblase-mediated alteration in plasma membrane asymmetry actually led to the increased cellular susceptibility to the group II subfamily of sPLA(2)s, several lines of evidence suggest that it does not entirely mimic their actions on cells after IL-1 signaling. Interestingly, coexpression of type IIA or V, but not X, sPLA(2) and phospholipid scramblase resulted in a marked reduction in cell growth, revealing an unexplored antiproliferative aspect of particular classes of sPLA(2).
我们最近报道，分泌型磷脂酶A2（sPLA2）肝素结合II族亚家族成员（IIA和V型）转染到293细胞后，优先响应白细胞介素-1（IL-1）释放[3H]花生四烯酸（AA），并作为与前列腺素生物合成功能偶联的“信号”磷脂酶A2发挥作用。在此我们表明，在293转染细胞中，这些II族亚家族sPLA2和X型sPLA2的行为方式不同，前者比后者更有效地与前列腺素生物合成途径偶联。X型sPLA2与细胞表面蛋白聚糖的结合极少，在有血清但无IL-1的情况下增加了[3H]AA和[3H]油酸的释放。IIA和V型sPLA2释放的AA均能有效转化为前列腺素E2，它们以肝素敏感的方式显著增强IL-1诱导的环氧化酶（COX）-2表达，而X型sPLA2缺乏增强COX-2表达的能力，因此除非将任何一种COX同工酶强行导入表达X型sPLA2的细胞中，否则其前列腺素E2生物合成反应较差。对负责扰乱质膜不对称性的磷脂翻转酶的研究表明，转染了磷脂翻转酶的细胞对IIA和V型而非X型sPLA2变得更敏感，能以不依赖IL-1的方式释放[3H]AA和[3H]油酸。因此，尽管磷脂翻转酶介导的质膜不对称性改变实际上导致细胞对sPLA2的II族亚家族的敏感性增加，但多项证据表明，它并不完全模拟它们在IL-1信号传导后对细胞的作用。有趣的是，IIA或V型而非X型sPLA2与磷脂翻转酶的共表达导致细胞生长显著降低，揭示了特定类别的sPLA2未被探索的抗增殖特性。
